Phase shifter for scanning antenna array



-L. A. KURTZ 2,908,906 PHASE SHIFTER' FOR SCANNING ANTENNA ARRAY Oct. 13,

Filed May-29. 1956 Louis A. Kurrz;

, Element Radiator INVENTOR.

ATTORNEY Louis A. Kurtz, Los Angeles, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application May 29, 1956, Serial No. 588,154 Claims. (Cl. 343-854) This invention relates to wave energy phase shifters and more particularly to wave energy coupling units which 7 provides a phase adjustable coupling between discrete elements of an antenna array and the mainfeed waveguide. 7

It is often desirable to derive a family of currents of specified magnitudes and continuously variable phases from wave energy propagated through a waveguide to excite discrete radiator elements of an array type antenna. The relative-magnitudes and phases of these excitation currents determine the character of the resulting radiation pattern. Once a desired radiation pattern has been obtained it has been found that by cyclically changing the relative phases of the excitation currents in a predetermined manner the direction of maximum radiation is also cyclically changed. Such a cyclic change may be used for scanning the radiated wave energy beam.

It is therefore an object of the present invention to provide a coupling unit to couple a discrete radiator element to a waveguide which coupling unit is adapted to provide means of adjusting the phase of the excitation current for the radiator element. 6

It is a further object of the present invention to pro-- vide a new type of wave energy phase shifter which is simple in construction and reliable in operation.

It is a still further object of the present invention to provide a new type of scanning antenna array by continuously changing the relative phases of, the excitation current feed ing the discrete radiator elements.

In accordance with the present invention, wave energy propagated through a waveguide is circularly polarized to provide the excitation for the. radiator element. The radiator element is provided with phase selective coupling means which means is responsive only to circularly polarized wave energy of a predetermined screw-sense". This coupling means is subjected to circularly polarized wave energy having the predetermined screw-sense. Circular polarization, as is well known to those skilled in the art, is a combination of two plane polarized waves in space and time quadrature .The coupling means absorbs the wave energy completely no matter what angular position the coupling plane occupies. However, the angular position between the coupling plane and the two plane waves comprising the circularly polarized wave'determines the phase of wave energy absorbed by the coupling means. A change of the angular positon of the coupling means changes the phase of the wave energy exciting the radiator element.

Fig. l is an exploded view of the phase shifter of this invention'and illustrates the application to array type antennas, and

Figs. 2 and 3 are modifications of the exciting means which couple the phase shifter of the present invention -to the main feed waveguide.

Referring now to Fig. 1, a main feed waveguide 10 and a cylindrical waveguide 12 are electrically coupled to one another by an exciting means 14. The exciting means 14 comprises a pair of elongated narrow slots 16 and 18 cluded in the Waveguide 10 and having their respective axes of elongation at right angles to one another. In other words, slot 16 is transverse and slot 18 is longitudinal. A radiator element 20 is electrically coupled to the cylindrical Waveguide 12 through a phase selective coupling means 22 comprising a coaxial waveguide 24 provided at one end with a pair of axial slots 26 and two pairs of radial dipoles 28 and 36 whose longitudinal axes are separated by an angle of 90 degrees. The coaxial waveguide 24 includes an outer conductor 31 and an inner conductor 32 which are electrically shorted by a radial shorting post 34. Support for the coaxial waveguide 24 in a rotatable and coaxial relation with the cylindrical waveguide 12 is provided by a support member 36 attached to the Waveguide closure member 38.

The operation of the phase shifter may be best explained by tracing the different modes of wave energy through the apparatus of Fig. 1. Wave energy propagated through the main feed waveguide 10 excites the slots 16 and 13 and causes radiation therefrom. The energy so radiated comprises two plane polarized waves which are in time and space quadrature with one another. The combination of the two plane polarized waves may therefore be defined as circularly polarized wave energy which is propagated by the cylindrical waveguide 12 and received by the pairs of dipoles 28 and 30. The distance between the plane defined by the four dipoles and the waveguide closure member 38'is substantially equal to one-quarter of the working wavelengths of the cylindn'cally polarized wave to provide a short circuit termination. The dipoles 28 and 30 are, therefore, excited by the circularly polarized wave as is well known to those skilled in the art and in turn excites the fundamental mode in the coaxial waveguide 22 which results in the propagation of wave energy to the radiator element 20. A change of the angular position of the dipoles 28 and 30 with respect to the slots 16 and 18 either advances or retards the phase of the fundamental mode excited in the coaxial waveguide 24 by a.

corresponding amount.

As is shown in Pig. 1, several radiators, each being coupled to the main feed waveguide 10 by a phase shifter of the present invention, may be placed next to one another to form an array. It is possible to continuously rotate the phase selective coupling means 22 to produce a scanning beam of wave energy. One way in which scanning may be induced to an antenna array of the type show in Fig. l is to couple each coaxial waveguide 24 to some rotation means and a suitable arrangement such as gears and rotate each phase selective coupling means with an angular velocity such that the magnitudes of the T angular velocity of adjacent coupling means are in arithmetic progression.

Fig. 2 illustrates a modification of the exciting means 14' of Fig. 1 wherein a coaxial waveguide 40 is coupled to the main feed waveguide 10 by having its inner conductor 42 telescoped into the waveguide in the manner well known in the art. The other end of the inner conductor 42 is electrically shorted to an outer conductor 43 by means of a radial shorting post 44. A pair of axial slots 46 are cut into the outer conductor 43 and two pairs of dipoles 48 and 56 are afifixed to the outer conductor in such a manner that their axes of elongation are displaced degrees with one another. This exciting means produces a circularly polarized wave in much the same way as the cross slots 16 and 18 of Fig. 1. To reduce reflections to a minimum, the distance between the plane defined by the four dipoles 48 and 50 and the surface of the main feed waveguide 10 should be substantially equal to one-quarter of the working wavelengths of the circularly polarized wave.

Fig. 3 illustrates a still further modification of exciting .means 14" of Fig. 1, wherein feed Waveguide 10 includes Patented Get. 13, 195.9

3 a pair of diagonal, narrow slots 52 and 54 oriented such that the longitudinal axes of each is at an angle of 45 degrees with the longitudinal axis of the main feed waveguide 10. The slots 52 and 54 are perpendicular to one another and form a point of intersection 56 which is preferably located at the point at which the magnetic field intensity I-I within the main feed waveguide has equal longitudinal and transverse components. The exciting means of Fig. 2 and Fig. 3 are both adapted to produce the circular polarized wave required for the operation of the phase shifter of Fig. 1, and either one may be substituted for the slots 16 and 18 of Fig. 1. The exciting means 14 of Fig. 1 has cerain advantages amongst which are a relatively large coupling coeflicient. By changing the size of the slots 16 and 18, the coupling coefiicient may be changed through a considerable range. Another advantage of the exciting means is that all refiections from the slots themselves cancel out so that no impedance mismatch is presented to a generator feeding the main feed Waveguide. Also since the slots 14 couple either screw-sense of circular polarization, any resonance Within the phase shifter is highly damped and does not affect either the linearity of phase shift With rotation ,or the input impedance of the phase shifter. The exciting means 14" of Fig. 3 has the advantage of cancelling the reflections from the slots 52 and 54 but onthe other hand the coupling coefiicient is limited by the fact that the crossover point 56' is fixed and therefore the length of the slots is geometrically limited by the waveguide wall. The exciting means 14" of Fig. 2 has certain characteristics inherent in probe coupling which at times may be found desirable. The phase shifter described above may be usefully employed Whenever wave energy is to be subjected to phase adjustment. Such phase adjustment may vary from a single adjustment of the phase or a continuous modulation of the phase depending on the end result desired.

What is claimed is:

1. A multi-elcment wave energy phase shifter to couple a plurality of radiator elements to a rectangular feed waveguide, said phase shifter comprising: a rectangular feed waveguide, a plurality of cylindrical waveguide sections, each being connected at right angles to one of the broad walls of said rectangular feed waveguide; exciting means coupling each of said cylindrical waveguide sec tions to said rectangular feed waveguide, said exciting means being responsive to the fundamental mode of wave energy in the rectangular waveguide and adapted to excite the circularly polarized mode of wave energy in said cylindrical waveguide sections; a pair of mutually perpendicular dipoles within each of said cylindrical waveguide sections defining a plane parallel to said broad wall for receiving said circularly polarized mode of wave energy, each of said pairs of dipoles being coupled to a dilferent radiator element; and means for rotating said pair of dipoles about an axis perpendicular to said plane, whereby the phase of the'wave energy excited by each of said pairs of dipoles within each of said radiator elements may be adjusted by a predetermined amount.

2. A multi-element wave energy phase shifter to couple a plurality of radiation elements to a feed waveguide, said phase shifter comprising: a rectangular feed waveguide; a plurality of cylindrical waveguide portions, each being connected at right angles to the same broad wall of said feed waveguide, each of said cylindrical waveguide portions being individually coupled to said feed Waveguide by means of a pair ofmutually perpendicular slots in said broad wall, each of said pair of slots coupling a predetermined amount of the TE -mode of wave energy in said feed waveguide to the TE circularly polarized mode of wave energy in one of said cylindrical waveguide portions and having a screw sense depending on the direction of propagation of the TE -mode in said feed waveguide, a plurality of pairs of mutually perpendicular dipoles coupled to each of said radiation elements and axially telescoped into a different one of said cylindrical waveguide portions, each of said dipoles being rotatably mounted with respect to its associated pair of slots and being responsive to Wave energy of a circularly polarized mode having a preferred screw sense, whereby the phase of the wave energy excited in each of said radiation elements is continuously adjustable by adjusting the rotational position of said dipoles.

3. The combination of claim 1 wherein each of said exciting means comprises a first slot extending transversely of said broad wall, a second slot spaced from said first slot and extending longitudinally of said broad wall, both of said slots communicating with said cylindrical waveguide section for coupling energy out of said rectangular wave guide and into said cylindrical waveguide. V

4. The combination of claim 1 wherein each of said exciting means comprises a coaxial waveguide means disposed on said broad wall andhaving a center conductor extending into said waveguide and a pair of dipoles, said dipoles being disposed on the end of said coaxial waveguide means and at right angles to each other for propagating circularly polarized wave energy from said rectangular waveguide into said cylindrical waveguide.

I 5. The combination of claim 1 wherein each of said exciting means comprises a pair of slots in said broad wall intersecting each other at substantially right angles whereby said slots will couple wave energy out of said rectangular waveguide and into said cylindrical waveguide.

References Cited in the file of jthis patent UNITED STATES PATENTS FOREIGN PATENTS 592,224 Great Britain Sept. 11, 1947 

